Process for the production of flake-form, crystalline particles having an aurivillius structure and the use thereof as effect pigments or substrates thereof

Abstract

A process for the production of flake-form, crystalline particles having an aurivillius structure, the use thereof as effect pigments or as substrates of effect pigments, furthermore, effect pigments which contain coated or uncoated flake-form, crystalline particles having an aurivillius structure as substrates, and the use thereof in various products.

1 . A process for the preparation of crystalline compounds having an aurivillius structure, in which the starting compounds are mixed with a salt mixture comprising NaCl and Na 2 SO 4  and optionally one or more assistants to give a homogenised salt matrix/oxide mixture and are heated at 800-1200° C. 
     
     
         2 . The process according to  claim 1 , in which Bi 2 O 3 , TiO 2 , and optionally a further oxide are mixed with a salt mixture comprising NaCl and Na 2 SO 4  and optionally one or more assistants to give a homogenised salt matrix/oxide mixture and are heated at 800-1200° C. 
     
     
         3 . The process according to  claim 2 , wherein the further oxide used is Fe 2 O 3 . 
     
     
         4 . The process according to  claim 1 , wherein the assistants used are one or more salts selected from the group consisting of Na 2 CO 3 , K 2 CO 3 , CaCO 3 , CaO, CaCl 2 , Na 4 P 2 O 7  and KBr. 
     
     
         5 . The process according to  claim 1 , wherein the salt mixture comprises assistants in an amount of 1-10 mol % of the amount of TiO 2  employed. 
     
     
         6 . The process according to  claim 1 , wherein the homogenised salt matrix/oxide mixture comprises 7-50% by weight of Bi 2 O 3  and TiO 2 . 
     
     
         7 . The process according to  claim 1 , wherein the homogenised salt matrix/oxide mixture is pressed to give moulded pieces. 
     
     
         8 . The process according to  claim 7 , wherein the moulded pieces are calcined in ceramic crucibles. 
     
     
         9 . The process according to  claim 8 , wherein the moulded pieces are calcined resting on corundum beads in ceramic crucibles. 
     
     
         10 . The process according to  claim 1 , wherein the compound prepared is Bi 4 Ti 3 O 12 . 
     
     
         11 . The process according to  claim 1 , wherein the compound prepared is Bi 5 Ti 3 FeO 15 . 
     
     
         12 . An effect pigments comprising coated or uncoated flake-form crystalline particles having an aurivillius structure. 
     
     
         13 . The effect pigments according to  claim 12 , wherein the flake-form crystalline particles having an aurivillius structure comprise Bi 4 Ti 3 O 12  or Bi 5 Ti 3 FeO 15 . 
     
     
         14 . The effect pigment according to  claim 12 , wherein the flake-form crystalline particles having an aurivillius structure are coated with one or more layers of oxides and/or oxide hydrates of aluminium, silicon, iron, zinc, zirconium, tin and titanium, and/or mixtures of these compounds. 
     
     
         15 . The effect pigments according to  claim 14 , wherein one or more organic and/or inorganic stabilisation layers have been applied to the flake-form crystalline particles having an aurivillius structure or to the outer metal oxide layer. 
     
     
         16 . An effect pigments comprising coated or uncoated flake-form crystalline particles having an aurivillius structure, wherein the flake-form crystalline particles having an aurivillius structure are produced by a process in which the starting compounds are mixed with a salt mixture comprising NaCl and Na 2 SO 4  and optionally one or more assistants to give a homogenised salt matrix/oxide mixture and are heated at 800-1200° C. 
     
     
         17 . A product selected from paints, coatings, automobile paints, powder coatings, printing inks, security printing inks, plastics, ceramic materials, glasses, paper, paper coatings, toners for electrophotographic printing processes, seed, greenhouse sheeting, tarpaulins, absorbers for the laser marking of paper and plastics, absorbers in the laser welding of plastics, cosmetic formulations, pigment pastes, pigment preparations and dry preparations, said product comprising an effect pigment comprising coated or uncoated flake-form crystalline particles having an aurivillius structure.